Spindle length is entirely dependant on what crank and bottom bracket you plan to use.
What you're shooting for is a particular chainline, and because that bike uses a fairly fat 34.9mm front derailleur (if I recall correctly), I personally would try for a slightly wide 50mm chainline (or if you go with a conventional 47.5mm -48mm chainline, have a 1mm bottom bracket spacer ready - the fat seat tube can sometimes present problems shifting into granny).
In any case, this could be 113mm on some crank/spindle combinations and 118 on others, including ISIS and most Octalink, all the way up to 126mm with LX 572 Octalink cranks.